mrtoo
@Skorp did give you a definitive explanation, your factual performance observations are just that, factual performance ...observations. you're doing the correlation does not imply causation thing we're all warned about.
as someone intimately familiar with DNS based content filtering, you'll never be able to touch unwanted content being served from the same domain wanted content is coming from. that's why you'll never ever be able to block pre/mid/post-roll ads on youtube with Private DNS. The ads you don't want to see and the video you do want to see all come from googlevideo.com, a reserve domain of google for storing video from youtube.com
I can't speak on PIA Mace, there are litany of reasons from better blocklists to geolocation but i can definitively say that it's not that Google Play Services isn't respecting your private dns, it's just that they've (cleverly) bundled what you want and what you don't want.
Look at the logs of your DNS as suggested and you'll see what we mean. The queries are being handled by your resolver. this is how i learnt about why you can't block googletagmanger and gstatic, the ads will go away but so will almost everything else with it.